Injection cylinders of die cast machines

ABSTRACT

In an injection cylinder of a die cast machine of the class wherein the piston of the cylinder is operated by pressurized fluid, the piston is moved in the forward direction for performing injection moulding by the expansion of gas contained in a gas accumulator and the piston is moved in the rearward direction by pressurized liquid. When the piston is moved in the forward direction the flow rate of the pressurized liquid discharged from the cylinder is controlled by means of a flow control valve.

United States Patent Segawa June 24, 1975 [5 INJECTION CYLINDERS 0F DIECAST 2.224.956 12 1930 Ernst et a1 1 92 134 x 1632.246 HI) 2 lchikawa etal 1 1 1 1 425/135 MACHINES T J 3,638.423 2/l972 Heijst .l 92/134 X {75]Inventor. Kazuyoshl Segawa, okyo, apan FOREIGN PATENTS OR APPLICATIONSAssigmcI Shim Kikai Kabushiki Kaisha- 1.1101783 2/1971 Germany .4 92 134Tokyo. Japan [22] Filed; N 5 [973 Primary Examiner-Robert B. ReevesAssistant E,ruminer-David Scherbel [2| I Appl' 412548 Attorney. Agent,or Firmwenderoth. Lind & Ponack [30] Foreign Application Priority DataABSTRACT Nov, 14 1972 Ja n ,4 47414 32 in an injection cylinder of a diecast machine of the class wherein the piston of the cylinder is operatedby [52] [1.5. CI. H 222/334; 94/l34; 222/372 pressurized fluid. thepiston is moved in the forward [5| Int. Cl 822d 17/04 direction forperforming injection moulding by the ex- [58] Field of Search 92/l34;222/334. 372; pansion of gas contained in a gas accumulator and the425/135; 94/134 piston is moved in the rearward direction by pressurizedliquid. When the piston is moved in the forward (56] References Cit ddirection the flow rate of the pressurized liquid dis- UNn-ED STATESPATENTS charged from the cylinder is controlled by means of a 2 11x1,134 7/1937 Hacssler .1 92 134 x flow comm Valve 1163.982 6/1939 Merciero. 92/134 X 6 Claims, 3 Drawing Figures C I I7 70 1 B 1% I\ l C 2PATENTEDJUN24 ms 3.891.126

SHEET 1 F I G.l PRIOR ART SHEET PATENTEDJUN 24 1975 FIG.3

INJECTION CYLINDERS OF DIE ('AST MACHI BACKGROUND OF THE INVE 'IION Thisinvention relates to a die cast machine. more particularly to a fluidpressure operated injection cylinder of a die cast machine capable ofoperating at a high speed and under a high pressure.

In a conventional liquid pressure circuit for operating the highpressure. high speed liquid pressure cylinder therein-after. merelytermed high speed cylinder) of a die cast machine. high pressure liquidis admitted into a vessel (hereinafter, merely termed a pressureaccumulator) sealed with compressed gas. the gas is com pressed to storeenergy in the pressure accumulator. and the high pressure liquid isadmitted into the high speed cylinder at a high speed through adirection change over valve. a speed regulator. etc. by the ex pansionof the gas in the pressure accumulator, thus moving at a high speed thepiston of the high speed cylinder. In such a conventional liquidpressure circuit. since the liquid flows at an extremely high speedthrough the conduit extending between the pressure accumulator and thehigh speed cylinder. an extremely severe \vater hammering phenomenonoccurs at the time when the moving piston comes to stop at which thekinetic energy of the piston is converted into pressure. Although thiswater hammering phenomenon continues only for an extremely shortinterval. the force of water hammering created in the injection cylinderof a die cast machine is transmitted to the molten metal introduced intoa metal mould. thus forming fins about cast products. In addition. suchwater hammer ing phenomena imparts an excessively large percussive loador surge pressure upon the liquid conduit. high pressure cylinder,component parts of the machine and the metal mould. For this reason. ithas been common to design the high speed cylinder to well resist againstsuch large surge pressure. Moreover. when the machine is operated at itsrated pressure. as there is a tendency of forming fins it has been thepractice to operate the machine under a pressure lower than the ratedpressure. To obviate these difficulties it has been proposed to use acylinder provided with an accelerator which transfers the liquid on theback pressure side of the piston to the high pressure side or a booster.However. these proposals are not satisfactory because the output thereofdecreases during operation.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved fluid operated injection cylinder for a die cast machine whichcan obviate difficulties mentioned above.

According to this invention. there is provided an injection cylinder ofa die cast machine of the class wherein the piston of the cylinder ismoved in the forward and rearward directions by admitting anddischarging pressuri/ed fluid into and out of the cylinder.characteri/ed in that there are provided a gas accumulator containingpressurized gas and connected to the cylinder on one side ofthe pistonfor tnoving the piston in the forward direction by the evpansion of saidpressuri/ed gas for performing injection moulding. a source ofpressurized liquid. means for admitting the pressuri/cd liquid into thecylinder on the opposite side of the piston to mine the same in therearward direction thereby compressing the gas in the gas accumulator.

l l l and means for controlling the flow rate of the pressurized liquidwhen it is discharged from the cylinder when the piston is moved in theforward direction.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. I is a diagrammatic representation of a typical prior art highpressure. large output liquid pressure cylinder;

FIG. 2 is a diagrammatic representation of the basic form of thisinvention; and

FIG. 3 is a diagram showing a modified embodiment of this inventionapplied to an injection cylinder of a cold chamber type die castmachine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I whichshows a typical construction of a prior art liquid pressure circuit forthe injection cylinder of a die cast machine. the liquid pressurecircuit shown therein comprises a cylinder 1 containing a piston 2 whosepiston rod 24: acts as a piston of an injection cylinder 20 forinjecting molten metal into a metal mould of a die cast machine. notshown. and an accumulator 3 containing pressurized liquid 21 andcompressed gas 22 thereabove. The pressurized liquid 2I is forced intoaccumulator 3 from a pump 23 via a conduit L and a check valve 6 tocompress gas 22. thus storing energy therein. When a change over valve 4is operated toward the left. the pressurized liquid 2I in accumulator 3flows into cylinder 2 via a flow control valve 5 and a conduit 7 to movepiston 2 toward the left. this flow of the liquid being assisted by theexpansion of the compressed gas 22, whereby the piston 2 is moved at anextremely high speed to inject the molten metal in the injectioncylinder 20 into the metal mould. Under these circumstances. the liquidin the cylinder 1 to the left of piston 2 is returned to a reservoir.not shown. via change over valve 4, and a stop valve 9 is held closed.After the metal mould has been filled v ith molten metal the piston 2acts to apply pressure to the cast metal. With this conventional liquidpressure circuit as the liquid flows through conduit 7 at an ex tremelyhigh speed during the forward or injection stroke of piston 2. whenpiston 2 is stopped after completely filling the metal mould to begin toapply pressure to the cast metal an extremely severe water hammeringphenomenon occurs.

FIG. 2 shows a diagram of the liquid circuit embodying the invention inwhich elements corresponding to those shown in FIG. I are designated bythe same reference characters. According to this invention. chamber Bofcylindcr I to the right ofpiston 2 is communicated with a sealed gasaccumulator 3 through a relatively thick conduit 71! and liquid underpressure is admitted into chamber C of cylinder 1 to the left of piston2 from pump 23 via a check valve 64:. change over valve 4 and a flowcontrol valve 50 which are connected in conduit 8. A check valve 10 isconnected in parallel with flow control valve Su and a pressure meter II is provided for accumulator ll. According to this invention. theliquid circuit is designed such that the force applied to the left-handside of piston 2 by the pressurized liquid is larger than that appliedto the righthand side of piston 2 by the compressed gas in accumulator3.

Under normal condition. stop valve 9 is held closed. I'nder theseconditions. upon operation of pump 23.

3 pressuri/ed liquid is admitted into chamber of piston 1 via thecircuit described abov e. Since L'hLL'l'v valve ll) is opened at thistime. piston I is moved quiclsly toward the right to compress the gas inaccumulator 3 and store energy therein until the forces acting upon bothsides of piston 2 become equal.

To operate the die cast machine. the change over valve 4 i switched tothe left to communicate chamber C with a drain. Then. the compressed gasin accumulator 3 expands to move. at a high speed. piston 2 toward theleft. ln the prior art liquid pressure circuit. as pressurized liquid inaccumulator 3 is used to operate piston 2. and hence the injectioncylinder of a die cast machine. an intense water hammeringphenomena wasinevitable when the movement of piston 2 is stopped as describedhcrcinabove. whereas according to this invention. since compressed gashaving a much smaller specific gravity than liquid has been stored inthe accumulator and is used to operate piston 2. the water hammeringphenomena would not occur because the gas is compressed when the pistonis stopped. When compared with liquid. the resistance of a conduit of agiven diameter to the flow of gas is evtremely small so that it ispossible to greatly increase the operating speed ofthe piston relativeto the prior art liquid circuit. The speed of the piston 2 during theforward stroke (to the left as viewed in FIG. 2 can be controlled by theflow control valve 5. The check valve 10 connected in parallel with flowcontrol valve 5 functions to eliminate the resis tance to the How ofliquid afforded by check valve 5 when the piston 2 is returned.

After advancing the piston 2. operation of the changeover valve 4introduces the pressurized liquid supplied by pump 23 into chamber C ofthe cylinder 1. the piston 2 to retract to the position shown in FIG. 2.During this retracting stroke. the gas in chamber B is pushed back intoaccumulator 3 to store energy. The purpose of check valve 6a is toprevent piston 2 from moving forwardly when pump 23 is stopped. Valve 9is opened for draining the accumulator 3.

FIG. 3 diagrammatically shows a modification of this invention appliedto the injection cylinder of a cold chamber type die cast machine. inwhich elements corresponding to those shown in FIG. 2 are designated bythe same reference characters. In this modification. a second llowcontrol valve Sb is added to operate the piston 2 at any one oftvvospeeds. There are also added electrically operated change over valves [2and I}. a second accumulator [4 connected to the output of the pumpthrough a stop valve 15. and a stop valve 16 for connecting theaccumulator 3 to the output of pump 23. In this embodiment. apredetermined quantity of liquid 2] is charged in accumulator 3 for thepurpose of adjusting the pressure of the gas contained therein.

When pump 23 is operated. the pressurized liquid is admitted into thechamber C of cylinder I via check valve 61! and change-ov er valve 4 toretract piston 2. The pressure of the gas contained in accumulator 3 andthe opening olllovv control valve l7 are predetermined such that thepressure applied to the molten metal in the mould increases gradually atthe cvtremc forward stroke of the piston 2. that is after the moltenmetal has been filed. (ias is filled in accumulator l4 under apredetermined pressure and valve 15 is normally held open. \'alvc I6 isclosed normally. In order to prevent piston 2 from moving in the forwarddirection vv hen pump 23 is stopped. as by interruption of electricsupply. a pilot chcclv valve It) is inserted between piston l and changeover valve 4. 'l he pilot check valve ltl is normally held open by theelectrically operated change over valve l2 so that upon interruption ofelectric supply. valve 10 is closed to prevent accidental forwardmovement of piston 2.

Then the change over valve 4 is switched to discharge the pressuri/edliquid in chamber through conduit 8. valves 10 and 4 and the low speedllovv control valve 5h. Accordingly. piston 2 is advanced at a low speedby the pressure of the gas in accumulator 3. Then changeover valve 13 isenergized to switch the How control valve to high speed side in. thusincreasing the speed of piston 2. Upon completion of the mouldingoperation. valve 4 is svvitched to the original state to again supplythe pressurized liquid from pump 23 to chamber (1 thus retracting piston2. Accordingly. the gas is again compressed in accumulator 3. Toaccelerate the returning motion of piston 2. valve 15 is opened normallyto cause the pressuri/ed liquid in accumulator H to assist pump 23.valve 16 is opened when it it desired to increase the gas pressure inthe accumulator.

This invention has the following advantages.

1 There is no water hannncring phenomena because the gas in theaccumulator provides cushioning ac tion.

I. The maximum speed of the piston is much higher than prior artdevices:

3. The device can produce a large output and can operate stably duringthe forward stroke;

4. The construction is simple and less susceptible to failure;

5. Consumption of the gas in the accumulator is minimal because there isno liquid in the accumulator. or even when liquid is filled therein.liquid is not moved. If the liquid is discharged and refilled into theaccumulator as in the prior art. gas will dissolv e in the liquid and becarried away therewith; and

6. Vibration ofthe piping and hence the noise caused thereby is small.

A die cast machine utili/ing the novel pressurized liquid circuit hasthe following advantages:

7. It is possible to east larger products with a machine of the samerating:

ts. It is possible to alleviate the casting condition and to improve thequality of the product and to decrease the number of rejects because thedie cast machine operates stably and because the pressure rises veryquickly at the final stage of the injection moulding:

9. The manutacturing cost of the castings is greatly reduced.

lt). It is highly safe and less noisy. and

l l The life ofthe machine and moulds can be greatly prolonged.

I claim:

I. la an injection cylinder of a die cast machine ofthc class whereinthe piston ofthe cylinder is moved in forward and rearward directions byadmitting and discharging pressuri/ed tluid into and out of saidcylinder. the improvement which comprises a gas accumulator containingpressuri/cd gas and a predetermined quantity of liquid. saidpredetermined quantity of liquid being used for adjusting the pressureof the gas contained in said accumulator. said gas accumulator havingsubstantially larger volume than said cylinder. at llow control valveconnected between said cylinder and said gas accumulator l'or admittingsaid gas into said cylinder thereby moving said piston in the forward direction by the expansion olsaid pressuri/ed gas for per forming diecasting. a source of pressuri/ed liquid. means operatively coupled l'oradmitting said pressurized liquid into said cylinder on the oppositeside of said piston to move the same in the rearward direction therehycompressing the gas in said gas accumulator. and means opcratnelycoupled for controlling the llovv rate of said pressurized liquid whilethe liquid is discharged from said cylinder when said piston is moved inthe forward direction 2. The injection cylinder according to claim 1wherein said tlovv controlling means is comprised of a valve and furthercomprising a check valve connected in parallel with said valve. saidcheck valve opening when the pressurized liquid is admitted into saidcylinder from said source.

3. The injection cylinder according to claim l which further comprisesan accumulator for said pressurized liquid and a normal open valveconnecting said liquid accumulator to said source of pressurized liquid.

4. The injection cylinder according to claim 1 wherein said flow ratecontrolling means comprises a plurality ol flow control valves forproviding different flow rates 5. The injection cylinder according toclaim I which further comprises a pilot check valve connected in theconduit of said pressurized liquid and an electrically operated valvemeans for normally holding said pilot valve in an opened state so thatsaid pilot check valve is closed when supply of electricity isinterrupted.

6. The injection cylinder according to claim I wherein the quantity ofsaid liquid contained in said gas accumulator is variable.

1. In an injection cylinder of a die cast machine of the class whereinthe piston of the cylinder is moved in forward and rearward directionsby admitting and discharging pressurized fluid into and out of saidcylinder, the improvement which comprises a gas accumulator containingpressurized gas and a predetermined quantity of liquid, saidpredetermined quantity of liquid being used for adjusting the pressureof the gas contained in said accumulator, said gas accumulator havingsubstantially larger volume than said cylinder, a flow control valveconnected between said cylinder and said gas accumulator for admittingsaid gas into said cylinder thereby moving said piston in the forwarddirection by the expansion of said pressurized gas for performing diecasting, a source of pressurized liquid, means operatively coupled foradmitting said pressurized liquid into said cylinder on the oppositeside of said piston to move the same in the rearward direction therebycompressing the gas in said gas accumulator, and means operativelycoupled for controlling the flow rate of said pressurized liquid whilethe liquid is discharged from said cylinder when said piston is moved inthe forward direction.
 2. The injection cylinder according to claim 1wherein said flow controlling means is comprised of a valve and furthercomprising a check valve connected in parallel with said valve, saidcheck valve opening when the pressurized liquid is admitted into saidcylinder from said source.
 3. The injection cylinder according to claim1 which further comprises an accumulator for said pressurized liquid anda normal open valve connecting said liquid accumulator to said source ofpressurized liquid.
 4. The injection cylinder according to claim 1wherein said flow rate controlling means comprises a plurality of flowcontrol valves for providing different flow rates.
 5. The injectioncylinder according to claim 1 which further comprises a pilot checkvalve connected in the conduit of said pressurized liquid and anelectrically operated valve means for normally holding said pilot valvein an opened state so that said pilot check valve is closed when supplyof electricity is interrupted.
 6. The injection cylinder according toclaim 1 wherein the quantity of said liquid contained in said gasaccumulator is variable.